Cooling arrangement for a power inverter

ABSTRACT

A power inverter has a housing enclosing inverter electronics including power transistors electrically coupled to a DC voltage input for supplying an AC voltage output. The inverter electronics are mounted on a circuit board that is fastened to the housing and the housing has a housing wall with air vents. A heat sink including cooling fins forming air channels is mounted on the circuit board and the power transistors have a heat transfer relationship with the heat sink. A fan is mounted in a further housing wall. The heat sink is disposed so that an air stream is created through the air channels of the heat sink and between the air vents and the fan for dissipating heat generated by the power transistors.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority of Provisional Patent Application Ser. No. 60/215,875 filed Jun. 30, 2000, the disclosure of said application being incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The invention relates to a cooling arrangement for an electronic circuit and in particular to a cooling arrangement for a power inverter, for example a power inverter of the type used for producing AC voltage for supplying power to portable electronic appliances such as laptop computers or handheld electrical tools.

[0003] A power inverter converts direct current (DC) voltage to alternating current (AC) voltage. Power inverters generally employ switching power semiconductors in an output stage for producing the AC voltage. The output power transistors generate heat that can place a limitation on the power output, because at high temperatures the power transistors will begin to fail. Therefore, mechanisms are employed for dissipating the heat to increase the level of current that can be handled by the power transistors. To protect the power transistors against overheating, a heat sensitive component, such as a thermistor is usually placed in the circuit with the output power transistors to open the circuit and cut off power to the output power transistors when a given temperature is reached. If insufficient heat dissipation is provided, the thermistor will open the circuit at relatively low levels of current, thus placing a limitation on the power output of the inverter.

[0004] In known inverters, the power transistors are electrically connected via a printed circuit board to an output terminal, usually in the form of a standard AC output receptacle, and are often physically connected to an interior surface of the inverter housing via a heat dissipation bar or rod. The inverter housing thus becomes hot to the touch, sometimes excessively so. Additionally, the physical connection of the output power transistors to the housing wall can become dislodged and the transistors themselves could be fractured if the inverter housing is jarred, for example if inadvertently bumped against a rigid surface.

[0005] There is thus a need to improve the heat dissipation of known power inverters and to better protect the output power transistors against physical damage.

SUMMARY OF THE INVENTION

[0006] It is an object of the invention to provide a power inverter with an improved cooling mechanism for the output power transistors.

[0007] It is a further object of the invention to increase the load capacity of known power inverters by improving the heat dissipation of the output power transistors.

[0008] It is still a further object of the invention to improve the arrangement for mounting the output power transistors in the inverter to better protect the power transistors against physical damage should the housing of the inverter be inadvertently jarred.

[0009] The above and other objects are accomplished in the context of a power inverter having a housing enclosing inverter electronics including power transistors electrically coupled to a DC voltage input for supplying an AC voltage output, wherein the inverter electronics are mounted on a circuit board that is fastened to the housing and the housing has a housing wall with air vents for admitting air into the housing, wherein in accordance with the invention there is provided: a heat sink including cooling fins forming air channels, the heat sink being mounted on the circuit board and the power transistors being fastened to the heat sink; and a fan mounted in a further housing wall opposite the housing wall with the air vents and being operative for blowing air out of the housing; wherein the heat sink is disposed between the air vents and the cooling fan so that a cross flowing air stream is created from the air vents through the air channels of the heat sink and out of the housing through the fan for dissipating heat generated by the power transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The sole Figure of the drawings is a perspective view of the interior of a power inverter including a cooling arrangement according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The Figure shows a power inverter 10 having a box-like housing 12 with a top wall and a side wall removed for viewing the interior of the power inverter. Housing 12, which is in part made of metal, for example extruded aluminum, encloses the electronics of the power inverter which are mounted on a circuit board 14 in a known manner. The electronics of the power inverter are known per se and do not form any part of the present invention.

[0012] Housing 12 includes one side wall 12 a having air vents 16 which admit air into the housing and an opposite side wall 12 b in which a cooling fan 18 is mounted for blowing air out of the housing so that an air stream is created between the air vents 16 and the cooling fan 18.

[0013] The inverter electronics include output power transistors 20 that are coupled between a DC voltage input 22 and an AC voltage output in the form of standard AC receptacles 24. The inverter electronics switch the output power transistors in a known manner for converting the DC voltage input to the AC voltage output.

[0014] A metallic heat sink 26 is mounted on circuit board 14 between air vents 16 and fan 18. Heat sink 26 includes a broad wall 28 to which the output power transistors are fastened and cooling fins 30 extending from wall 28 and forming parallel air channels 32. Heat generated by the output power transistors is thus transferred to heat sink 26 and dissipated to the air in channels 32.

[0015] In operation, fan 18 creates a cross flowing air stream which enters the housing through vents 16, flows through channels 32 and out of housing 12 through fan 18. Heat generated by the output power transistors is thus dissipated by the heat sink to the cross flowing air stream and removed from the housing, creating an efficient cooling arrangement for reducing the temperature inside the housing, and permitting a higher electrical load capacity for the power electronics, and in particular the output power transistors.

[0016] Additional benefits from the cooling arrangement of the invention result from the fact that the output power transistors are not directly in contact with the inside wall of the extruded aluminum housing. First, this reduces the temperature of the housing to the touch. Additionally, since the output power transistors are connected to the heat sink which is in turn supported by the circuit board, the output power transistors are mechanically isolated from the housing and are less likely to be damaged due to mechanical shock to the housing which could occur, for example, during shipping.

[0017] The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art, that changes and modifications may be made without departing from the invention in its broader aspects, and the invention, therefore, as defined in the appended claims, is intended to cover all such changes and modifications that fall within the true spirit of the invention. 

What is claimed is:
 1. In a power inverter having a housing enclosing inverter electronics including power transistors electrically coupled to a DC voltage input for supplying an AC voltage output, wherein the inverter electronics are mounted on a circuit board that is fastened to the housing and the housing has a housing wall with air vents for admitting air into the housing, the improvement comprising: a heat sink including cooling fins forming air channels, the heat sink being mounted on the circuit board and the power transistors being fastened to the heat sink; and a fan mounted in a further housing wall opposite the housing wall with the air vents and being operative for blowing air out of the housing; wherein the heat sink is disposed between the air vents and the cooling fan so that a cross flowing air stream is created from the air vents through the air channels of the heat sink and out of the housing through the fan for dissipating heat generated by the power transistors. 